An existing center-line butterfly valve includes a valve body, wherein a fluid passage is provided in the valve body, a valve plate of which an outer surface is covered with an elastic sealing layer is provided within the fluid passage, an upper portion of the valve plate is dynamically connected with a driving shaft which is rotatably connected to the valve body, and a lower portion of the valve plate is rotatably connected with a supporting shaft which is connected to the valve body. The driving shaft drives the valve plate to rotate centered with an axis of the driving shaft and the supporting shaft, to achieve opening and closing. The elastic sealing layer covered on an outer periphery of the valve plate is extruded and elastically deformed by the valve plate and an inner wall of the fluid passage, to achieve sealing upon being closed. The center-line butterfly valve of the structure above mainly has the following drawbacks: the first drawback is that it is highly demanding on rigidity of the valve body and a valve shaft; if the rigidity of the valve body is insufficient, deformation may occur under action of fluid pressure, causing lax contact between the valve body and the valve plate and consequently leakage; if the rigidity of the valve shaft is insufficient, the valve body will be displaced axially along the fluid passage under the action of fluid pressure, thereby causing valve leakage; in order to enhance the rigidity of the valve body and the valve shaft, an amount of material in use for the valve body and the valve shaft has to increase, which causes a large weight for the valve body and the valve shaft, thereby incurring a high manufacturing cost. The second drawback is that a larger pressure on the elastic sealing layer not only causes the valve to have large opening and closing torques, but also aggravates wear of the elastic sealing layer, which shortens a service life of the valve and is not suitable for a pipeline system that is opened and closed frequently; besides, a self-weight of the valve plate also exacerbates wear and makes the opening and closing more difficult.